1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium capable of recording information at a high density, a recording method therefor, and a magnetic recording apparatus provided with the magnetic recording medium.
2. Description of the Related Art
As the information network is developed and the multimedia comes into the widespread use, the magnetic disk apparatus, which is the major information-recording apparatus for supporting such circumstances, encounters important problems of the realization of small size, low price, and large capacity and the improvement in reliability. In such a situation, the perpendicular magnetic recording medium is noticed, which is strongly resistant to the thermal fluctuation as compared with the in-plane or longitudinal magnetic recording medium and on which the recording can be performed at a high density. As for the perpendicular magnetic recording medium, those suggested as the recording layer include, for example, CoCr-based polycrystalline films, so-called multi layer thin films obtained by alternately stacking or laminating multiple layers of Co and Pd, and superlattice alloy films.
In relation to the perpendicular magnetic recording medium, the present applicant has disclosed a structure in which an in-plane magnetize layer is added in contact with a recording layer in order to form fine and minute magnetic domains in Japanese Patent Application Laid-open No. 2002-216333. In this structure, the recording layer and the in-plane magnetized layer are exchange-coupled. The magnetization is stabilized while being slightly inclined with respect to the film surface in the vicinity of the interface between the both layers. Therefore, the magnetization of the recording layer includes an in-plane component. On this condition, when an external magnetic field, which is in a direction opposite to that of the magnetization of the recording layer, is applied, the magnetization of the recording layer is reversed more easily by the external magnetic field, because the magnetization of the recording layer includes the in-plane component. Accordingly, the magnetic field to start the magnetization reversal is lowered.
However, it is necessary that the thermal stability of the recording magnetic domain is further improved in a high density recording area of not less than 100 gigabits/square inch (Gb/in2), especially not less than 500 gigabits/square inch. Japanese Patent Application Laid-open No. 2002-216333 described above discloses nothing about the enhancement of the stability of the recording magnetic domain against the thermal disturbance to be caused when the high density recording is performed as described above. That is, the patent document neither teaches nor suggests the condition and the medium structure to simultaneously exhibit such functions intrinsically required for the realization of the high density that the recording is assisted and the recorded magnetic domains are stabilized during the storage so that the information is hardly erased, especially the relationship between the residual magnetization in the perpendicular direction and the coercive force (coercivity) in the in-plane direction of the magnetic recording medium.